Technical Field
The present disclosure relates to catalyst support for electrochemical fuel cells.
Description of the Related Art
Fuel cell systems are currently being developed for use as power supplies in numerous applications, such as automobiles and stationary power plants. Fuel cell systems offer the promise of economically delivering power with environmental and other benefits. However, to be commercially viable fuel cell systems need to exhibit adequate reliability in operation, even when the fuel cells are subjected to conditions outside the preferred operating range. For a proton exchange membrane (“PEM”) fuel cell to be used commercially in either transportation or stationary applications, 5,000 to 40,000 hours of operation may be required.
A fuel cell may include a PEM interposed between two electrodes; namely, a cathode and an anode. Both the anode and cathode typically include a gas diffusion layer and a catalyst layer. The anode, PEM and cathode, or membrane electrode assembly (MEA), is usually disposed between flow field plates, which allow the ingress and egress of reactant and reaction product to the catalyst layer. The MEA and flow field plates, known as a fuel cell, may be coupled in series to form a fuel cell stack.
At the anode, fuel (typically in the form of hydrogen gas) reacts at the electrocatalyst in the presence of the PEM to form hydrogen ions and electrons. At the cathode, oxidant (typically air) reacts in the presence of the PEM at the electrocatalyst to form anions. The PEM isolates the fuel stream from the oxidant stream and facilitates the migration of the hydrogen ions from the anode to the cathode, where they react with anions formed at the cathode. The electrons pass through an external circuit, creating a flow of electricity. The net reaction product is water. The anode and cathode reactions in hydrogen gas fuel cells are shown in the following Equations (1) and (2):H2→2H++2e−  (1)½O2+2H++2e−→H2O  (2)
The catalyst layer is typically comprised of a catalyst, supported on a catalyst support. Fuel cell catalysts known in the art include platinum and platinum-ruthenium. Fuel cell catalyst supports known in the art include carbon black, including furnace black and acetylene black. Such catalyst supports are employed for their relatively low cost, good electronic conductivity, and their ability to be made sufficiently porous to allow the passage of reactant and reaction product to and from the reaction site. In practice, significant difficulties have been encountered with regard to consistently obtaining sufficient operational lifetimes for fuel cells due, in part, to oxidation of the catalyst support at the anode and/or cathode.
Accordingly, there remains a need in the art for improved catalyst supports for electrochemical fuel cells, particularly with regard to mitigating and/or eliminating oxidation of the catalyst support. The present disclosure fulfills this need and provides further related advantages.